1. Technical Field
The present invention pertains to methods and apparatus for underwater communication and, more particularly, to the transmission of acoustic vibrations to the cochlea through a tooth of a diver.
2. Discussion of the Prior Art
Communication among divers and between divers and surface support personnel is essential to the efficiency and safety of virtually all undersea operations. Elaborate systems of hand signals have been used where light and distance permits but the range of utility is small. Coded pulses offer more range but are inadequately slow and distracting. One approach to voice communication has been developed that transmits mechanically generated acoustic sound energy directly through the water to intended receivers. A second approach has been to use electronics to transfer signals, by direct wire through ultrasonics or electromagnetic radiation.
Mechanical systems of underwater voice communication must provide an impedance match between the acoustic energy of the speaker's voice and the acoustic energy generated in the water for sound transmission, as described for example, by U.S. Pat. No. 4,071,110 (Payne). The unamplified range of such devices is limited and both the comfort of the diver and the intelligibility of the communication are compromised by the requirement that a bit or rigid mouthpiece, for instance a metal rod, be gripped or clenched tightly by the teeth of the diver in order to properly transmit and receive audio signals.
Existing electronic underwater communications systems require that both the ears and mouth are surrounded by air. The bulkiness of the air-conduction earphones and the distortion resulting from the interaction of underwater pressure on the air column in the outer human ear have hindered the usefulness and acceptance of these devices.
An alternative approach, imparting vibrations to the skull for osseus transmission through the skull bones to the cochlea, and hence as signals via the auditory nerve to the brain, is exemplified by U.S. Pat. No. 5,033,999 (Mersky). That bone conduction device uses the teeth as the input site into the skull. Such tooth related devices have not been intended or adapted for use with an underwater breathing apparatus, however, instead having focused on the advantage of repeatable skull coupling to achieve better speech intelligibility, comfort and improved cosmetics. The issues inherent to maintaining an efficient and effective vibration-transmitting engagement between the tooth and the vibration input device without placing unacceptably distracting demands on the diver while simultaneously permitting intelligible articulation despite the intrusion of breathing support apparatus has not been addressed.